Field of the Invention
The present invention relates to an automatic focusing apparatus for, e.g., a camera and, more particularly, to an automatic focusing apparatus using auxiliary light.
Related Background Art
One of conventional methods for a focusing apparatus of a camera is such that a light beam from an object to be photographed, which is transmitted through a photographing lens, is received and stored by a charge-storage photoelectric conversion element such as a CCD. In this case, if luminance of the light beam is determined to be low, auxiliary light is radiated on the object to be photographed, and charge is stored again. Then, a focusing state of the photographing lens is detected in accordance with an output, and the photographing lens is driven on the basis of a detection result. In many cases, in order to protect an auxiliary light source and to save energy, the number of radiations of the auxiliary light is limited to a finite one.
In addition, various operation modes of a camera focusing apparatus are known such as a so-called "one-shot mode" in which once an in-focus state is obtained, focusing is not performed until an external member is operated, and a so-called "servo mode" in which focusing is continuously performed regardless of a previous focusing state.
However, when the above servo mode is selected by a user and at the same time auxiliary light is used because luminance of an object to be photographed is reduced, time corresponding to the number of radiations described above passes while focusing is continuously performed by radiating the auxiliary light in accordance with control in the servo mode. As a result, the auxiliary light is no longer radiated, thereby significantly degrading operability.
In addition, the auxiliary light source is turned on when luminance is determined to be low as described above. When the auxiliary light source is turned on, luminance is increased thereby. However, the auxiliary light source may be undesirably turned off although a focusing state need be detected under emission of the auxiliary light.
Furthermore, when so-called continuous photographing is to be performed by a camera incorporating the above automatic focusing apparatus, automatic focusing and photographing are repeatedly performed. In this case, since the auxiliary light for focusing is emitted for a short time interval every time focusing is performed, time corresponding to the above finite number of emissions may pass soon.